The present invention relates to methods of controlling the timing of spark ignition for spark ignition internal combustion engines, and more particularly the invention relates to such a method in which the time average value of the magnitude of engine vibration is compared with the instantaneous value of the engine vibration to detect knocking in the engine and the timing of spark ignition of the engine is controlled in accordance with the comparison result.
With known spark ignition internal combustion engines, generally it is preferable to set the spark ignition timing at MBT (Minimum Spark Advance for Best Torque) so as to obtain the maximum torque. However, when the engine load increases, the spark ignition timing which is dependent on the MBT characteristic will be advanced with respect to a threshold spark ignition timing at which the engine is caused to knock.
To prevent the occurrence of knocking in an engine, as for example disclosed in U.S. Pat. No. 4,002,155, it has been found to be effective to compare the average value with an instantaneous value of the magnitude of the engine vibration to detect the presence of knocking in the engine and thereby to retard the spark ignition timing upon detection of knock. Of course, it is necessary to accurately measure the average value of the engine vibration so as to ensure accurate knocking detection.